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Some patient positions employed to facilitate neurosurgery can compromise cerebral venous drainage and lead to increased intracranial pressure, intraoperative bleeding, and brain bulge. This study evaluated the impact of different surgical positions on internal jugular vein (IJV) flow as a measure of cerebral venous drainage and on optic nerve sheath diameter (ONSD) as an indirect assessment of intracranial pressure.Ninety patients scheduled for elective primary brain tumor resection surgery were included in 3 groups of 30 each according to the surgical position: supine, prone, or lateral. Bilateral IJV flow was recorded at 3-time points: before the induction of anesthesia in the supine position (T0), 10 minutes after the induction of anesthesia in the supine position (T1), and 10 minutes after final positioning (T2). The ONSD was measured at T1 and T2.Mean IJV flow decreased from baseline by 36%, 10% and 38% in the supine, prone and lateral position groups, respectively. Mean IJV flow was 1005.9±463 mL/min versus 634.7±245 mL/min (P=0.036) in Group S, 752.5±384.8 mL/min versus 672.3±391.0 mL/min (P=0.002) in group P, and 831.8±337.4 mL/min versus 514.4±305.3 mL/min (P0.001) in group L at T0 and T2, respectively. Mean ONSD did not change between T1 and T2 in Groups S and P but increased in group L (P0.05).Mean IJV flow decreased from baseline following the final neurosurgical positioning. Ultrasound-guided assessment of IJV flow could be a useful tool to quantify position-related changes in IJV drainage.